Gas chromatography has proven to be a reliable and highly useful tool in separating subject compounds from potentially interfering compounds which would otherwise make it difficult to quantify and identify subject compounds in an atmospheric sample. Nonetheless, such compounds are often found in only trace amounts which makes their analysis very difficult. When the compounds are hazardous or lethal, it is imperative that they be detected before a dangerous concentration level is reached. It is known to use a preconcentrator step employing cryogenic trapping and or an adsorbent in order to detect trace amounts of such compounds as organosulfur or organophosphorus compounds. Unfortunately, even with these preconcentrator steps, the detectable quantities of the subject compounds remain above desirable levels. One limiting factor in reducing the detectable quantity has been the internal losses in systems designed to sample and detect trace compounds in the atmosphere.
Exemplary of the problem is U.S. Pat. No. 4,399,688 to Dennis. Dennis recognized that compounds of interest such as air pollutants may react with sample lines or with other components during transport for analysis. Dennis, however, was working with concentrations of 1 part per billion or greater and thus determined that conduit runs of several hundred feet between his concentrator and analyzer were acceptable and that such preconcentration was of no benefit unless the sample site was more than 10 feet from the analyzer. Accordingly, Dennis also determined that any suitable valving system could be used in the concentrator system, and preferenced a diaphragm switching valve. While such devices as Dennis may be suitable for concentrations greater than 1 part per billion, they are unsuitable for use in detecting lower concentrations of certain compounds.